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Re: [PATCH 64/78] dm: simplify flush_bio initialization in __send_empty_flush



On 11/16/20 3:57 PM, Christoph Hellwig wrote:
We don't really need the struct block_device to initialize a bio.  So
switch from using bio_set_dev to manually setting up bi_disk (bi_partno
will always be zero and has been cleared by bio_init already).

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
  drivers/md/dm.c | 12 +++---------
  1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 54739f1b579bc8..6d7eb72d41f9ea 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1422,18 +1422,12 @@ static int __send_empty_flush(struct clone_info *ci)
  	 */
  	bio_init(&flush_bio, NULL, 0);
  	flush_bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC;
+	flush_bio.bi_disk = ci->io->md->disk;
+	bio_associate_blkg(&flush_bio);
+
  	ci->bio = &flush_bio;
  	ci->sector_count = 0;
- /*
-	 * Empty flush uses a statically initialized bio, as the base for
-	 * cloning.  However, blkg association requires that a bdev is
-	 * associated with a gendisk, which doesn't happen until the bdev is
-	 * opened.  So, blkg association is done at issue time of the flush
-	 * rather than when the device is created in alloc_dev().
-	 */
-	bio_set_dev(ci->bio, ci->io->md->bdev);
-
  	BUG_ON(bio_has_data(ci->bio));
  	while ((ti = dm_table_get_target(ci->map, target_nr++)))
  		__send_duplicate_bios(ci, ti, ti->num_flush_bios, NULL);

Ah, thought as much. I've stumbled across this while debugging blk-interposer.

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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